Pion Decay-Mode Tagging in a Plastic Scintillator Using COPPER 500MHz FADC

PIENU experiment is going to be carried out in TRIUMF to measure the ratio of pion decay rates, R = Gamma(pi⁺ rarr e⁺nu_e)/Gamma( pi⁺ rarr mu⁺nu_mu), within 0.1% uncertainty. In order to achieve the precision, muon identification with waveform analysis in the target scintillator is necessary. Due to the short lifetime of pions, muon pulses tend to overlap onto the pion pre-pulses. Thus waveform analysis with high frequency flash ADC (FADC) is essential for the identification of the muon events. We use 500 MHz flash ADC (FADC) on COPPER system, which was developed in KEK, to readout waveform of the target scintillator. Muon pulse identification capability of the FADC system was investigated by artificial pulses simulating PMT signals.